This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-253882, filed Aug. 24, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a cathode-ray tube (CRT) apparatus, and more particularly to a color cathode-ray tube apparatus with an electron gun assembly capable of performing dynamic astigmatism compensation.
2. Description of the Related Art
In these years, self-convergence in-line type color CRT apparatuses, each of which can self-converge three in-line electron beams on the entire area of a phosphor screen, have widely been used. In this type of color CRT apparatus, an electron beam, which has passed through a non-uniform magnetic field, suffers deflection aberration. As is shown in FIG. 1A, for example, an electron beam 12 receives a force in the direction of arrows 13 due to a pin-cushion-shaped horizontal deflection magnetic field 11. Consequently, as shown in FIG. 1B, the beam spot 12 of the electron beam deflected onto a peripheral portion of the phosphor screen deforms, thus seriously degrading the resolution.
Owing to the deflection aberration suffered by the electron beam, the electron beam is vertically over-focused while it is horizontally spread. As a result, the beam spot on the peripheral portion of the phosphor screen has a horizontally deformed core portion 14 with high luminance and a vertically spread halo portion 15 with low luminance.
There are known some means for solving the problem of degradation in resolution. For example, electron gun assemblies have a common structure comprising first to fifth grids. The electron gun assembly includes an electron beam generating section, a quadrupole lens, and a main lens, which are formed along the axis of travel of electron beams. The quadrupole lens is composed of the third and fourth grids disposed adjacent to each other. The third and fourth grids, respectively, have three vertically elongated non-circular electron beam passage holes and three horizontally elongated non-circular electron beam passage holes in their mutually opposing surfaces.
FIG. 2 shows an equivalent optical model for illustrating correction of deflection aberration by the electron gun assembly. When the quadrupole lens is not made to function, an electron beam 800 travels through a main lens 803 and a deflection magnetic field 804, as indicated by broken lines. The electron beam 800 deflected on a peripheral portion 805 of the phosphor screen is horizontally under-focused and vertically over-focused. Consequently, the resolution greatly deteriorates.
When the quadrupole lens is made to function, the effect of deflection aberration due to the deflection magnetic field 804 is decreased, as indicated by solid lines. An electron beam 801 deflected on the peripheral portion 805 of the phosphor screen creates a beam spot with a suppressed halo portion.
Even if the above correction means is provided, however, the deflection aberration due to the deflection magnetic field is very serious. Although the halo portion of the beam spot may be eliminated, the horizontal deformation of the core portion cannot be corrected. This occurs mainly due to the difference in incidence angle between horizontal and vertical directions of the electron beam that strikes the phosphor screen.
Specifically, the electron beam is affected differently in the horizontal and vertical directions owing to the quadrupole lens and deflection magnetic field. Thus, the horizontal incidence angle ax  less than  less than  the vertical incidence angle ay. As a result, the horizontal magnification Mx  greater than  greater than  the vertical magnification My, according to the law of Lagrange-Helmholz. Consequently, the beam spot of the electron beam focused on the peripheral portion of the phosphor screen is horizontally deformed.
There are known some color CRT apparatuses capable of correcting the horizontal deformation. An electron gun assembly applied to these CRT apparatuses basically comprises first to seventh grids and includes an electron beam generating section, a first quadrupole lens, a second quadrupole lens and a main lens, which are arranged in the direction of travel of electron beams. The first quadrupole lens is formed by providing the third and fourth grids, which are disposed adjacent to each other, with three horizontally elongated non-circular electron beam passage holes and three vertically elongated noncircular electron beam passage holes in their mutually opposing surfaces. The second quadrupole lens is formed by providing the fifth and sixth grids, which are disposed adjacent to each other, with three vertically elongated non-circular electron beam passage holes and three horizontally elongated non-circular electron beam passage holes in their mutually opposing surfaces.
The lens action of the first quadrupole lens varies in synchronism with the variation in the deflection magnetic field, thereby correcting the image magnification of the electron beam incident on the main lens. The lens actions of the second quadrupole lens and the main lens vary in synchronism with the variation in the deflection magnetic field, thereby preventing the electron beam, which will ultimately be deflected on the peripheral portion of the phosphor screen, from being greatly deformed by the deflection aberration due to the deflection magnetic field.
FIG. 3 shows an equivalent optical model for illustrating correction of deflection aberration by the electron gun assembly. Specifically, a first quadrupole lens 901 controls the image magnification of an electron beam 900 incident on a main lens 903. A second quadrupole lens 902 varies the focus condition of the main lens 903, thus correcting deflection aberration due to a deflection magnetic field 904 and focusing the electron beam 900 on a peripheral portion 905 of the phosphor screen. Thereby, compared to a conventional dynamic focus electron gun assembly with a single quadrupole lens, the horizontal deformation can be eliminated and the electron beam can be focused on the peripheral portion of the phosphor screen more appropriately.
The use of the above-described double quadrupole lens structure, however, increases the incident angle in the horizontal direction, at which the electron beam to be focused on the peripheral portion of the phosphor screen enters the main lens section. Thus, the electron beams becomes more susceptible to the effect of spherical aberration of the main lens. In short, the beam spot at the peripheral portion of the phosphor screen has a horizontal halo portion.
Compared to the structure shown in FIG. 2 wherein the quadrupole lens is disposed in front of the main lens, the structure shown in FIG. 3, wherein the double quadrupole lenses are disposed in front of the main lens, has the following problem: the trajectory of the electron beam varies both in the horizontal and vertical directions. This requires optimization of the shape of the first quadrupole lens, optimization of the shape of the second quadrupole lens, and re-designing of the main lens system.
In general terms, the dynamic focus electron gun assembly performs focus adjustment by adjusting an external voltage. In the case of the structure shown in FIG. 2, the optimal focus adjustment can be made by varying the quadrupole lens 802 and main lens 803. However, in the case of the structure shown in FIG. 3, the focus adjustment is affected by the variation of the first quadrupole lens 901, second quadrupole lens 902 and main lens 903. As a result, the lens functions are complicated, and it is difficult to set an optimal focus voltage.
Moreover, in the case of the structure shown in FIG. 3, the shape of the electron beam passage hole formed in each of the electrodes constituting the first quadrupole lens differs from the shape of other holes. Consequently, in the electron gun assembling steps, center rods 52, 53 and 54 of an electron gun assembling jig 51 shown in FIG. 4 may not fit in the electron gun passage holes of the electrodes. This requires re-designing of the jig.
The present invention has been made in consideration of the above problems, and the object of this invention is to provide a cathode-ray tube apparatus having an electron gun assembly, which requires no re-designing of a main lens system, can easily perform focus adjustment, requires no re-designing of a jig at the time of assembling an electron gun, and can obtain good image characteristics over the entire area of a phosphor screen.
In order to solve the problems and achieve the object, a cathode-ray tube apparatus of claim 1 comprises: an electron gun assembly including an electron beam generating section which generates an electron beam, and a main lens section which focus an electron beam generated from the electron beam generating section onto a phosphor screen; and a deflection yoke which generates deflection magnetic fields for deflecting and scanning the electron beam emitted from the electron gun assembly in a horizontal direction and a vertical direction, wherein the electron gun assembly includes a focus electrode supplied with a focus voltage of a first level and constituting a part of the main lens section, a first dynamic focus electrode supplied with a dynamic focus voltage obtained by superimposing an AC component, which varies in synchronism with the deflection magnetic fields, upon a reference voltage close to the first level, and constituting a part of the main lens section, a second dynamic focus electrode supplied with the dynamic focus voltage and disposed in a front stage of the main lens section, and an anode supplied with an anode voltage with a second level higher than the first level, at least two auxiliary electrodes are disposed adjacent to the second dynamic focus electrode, the at least two auxiliary electrodes are connected via a resistor disposed near the electron gun assembly, and the focus electrode and the first dynamic focus electrode are disposed adjacent to each other.
A cathode-ray tube apparatus of claim 3 comprises: an electron gun assembly including an electron beam generating section which generates an electron beam, and a main lens section which focus an electron beam generated from the electron beam generating section onto a phosphor screen; and a deflection yoke which generates deflection magnetic fields for deflecting and scanning the electron beam emitted from the electron gun assembly in a horizontal direction and a vertical direction, wherein the main lens section of the electron gun assembly includes a focus electrode supplied with a focus voltage of a first level, a dynamic focus electrode supplied with a dynamic focus voltage obtained by superimposing an AC component, which varies in synchronism with the deflection magnetic fields, upon a reference voltage close to the first level, and an anode supplied with an anode voltage with a second level higher than the first level, the electron gun assembly further includes at least two auxiliary electrodes disposed between the focus electrode and the dynamic focus electrode, and the at least two auxiliary electrodes are connected via a resistor disposed near the electron gun assembly.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.